Basic question!

JavaScript
1

Hello all! I’m (very) new to coding, so bear with me.

I’m currently doing the JAVASCRIPT course, and i’m stuck on this:

// Setup

var a;

var b = 2;

// Only change code below this line

a = 7;

b = a;

Whenever i put a = b; instead of b = a; the code doesn’t work and i can’t figure out why. I’m also confused that - although b was defined as = 2, when a = 7 and b = a, it seems b has values both 2 and 7?

Any help greatly appreciated. Thanks!

Matt

2

Hi @matthurry. Welcome to FCC. In programming ,= is an assignment operator. When you say a = b, that can be interpreted as get the value of variable b and assign it to variable a. Similarly b = a is interpreted as get the value of variable a, assign it to variable b. Therefore a = b and b = a are not the same. That is why your test is failing.

What is happening above?

  1. var a . You have declared a variable called a but not yet assigned it a value.
  2. var b = 2 .Here you have declared variable b and assigned it a value of 2 (assigning value to a variable is also referred to as initializing the variable).
  3. a = 7. Here you are assigning variable a the value 7 (initializing it with the value 7).
  4. b = a. Interpreted as getting the value of variable a (which is 7) and assigning it to variable b. Making b to evaluate to 7 just like a(Remember b was initialized to 2).
  5. However if you are to say a = b. That is interpreted as get the value of b which is 2 assign it to a so that a also evaluates to 2.

HAPPY CODING

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3

Hi nibble, thanks for answering so quickly.

Yep that’s great - thanks for that. It did explain that x = y statements are read from right to left, but i was still reading them at mathematical statements (where of course x = y and y = x are the same).

Just a quick follow up if you don’t mind:

Is the line var b = 2; now redundant? Because of course, we know that b = 7. Since i have redefined it as 7, can i leave this statement that initialises b as 2?

Thanks again,
Matt

1 Like
4

I am glad the answer was helpful.
For a variable to be assigned a value, it must be declared. For example:

var a;  //Declaration of variable a
a = 1; //Assigning value 1 to a

OR
You declare and assign a value to a variable concurrently. Like

 var a = 1; //declare variable a and assign value 1 to it immediately

NO. That line is not redundant because it is where b was declared and immediately assigned a value (2). If you remove it, you would be using b without declaring it (which is UNFORGIVABLE SIN when programming using JavaScript- I don’t know about other programming languages). Good programming practice in Javascript dictates that you should NEVER assign a value to a variable which you haven’t declared.

EDIT

Though not recommended, even if you remove the line var b = 2 the code will still work in this particular case (In some it will raise an error).
WHY ? You will answer that in more advanced sections of Javascript. Just learn the basics for now.
NB: IT WILL FAIL THE TEST HERE ON FCC if you do that.

5

it is above the line that say // Only change code below this line
so, no, you can’t change it.

in real projects you would declare the variable to something, then use it, then change it to something else. But this is a practice exercise, where you see small examples, which often you would not see in real code.

1 Like
6